Method of adding lead to steel with lead oxide slag

ABSTRACT

High lead content of uniformly dispersed; finely divided, particles is obtained in cast steel through the dissolution of lead in the steel when molten. Lead is made available for dissolution by the reducing action of steel constituents upon lead oxide (PbO) that is contained in a covering slag.

United States Patent .1191

Thomas et a].

12/1970 McClellan 75/129 [111 3,820,982 1 June 28, 1974 3,567,204 3/1971 Ando 75/61 3,573,895 4/1971 Ostberg 75/61 3,664,826 5/1972 Kraemer.... 75/129 3,671,224 6/1972 North 75/129 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg Attorney, Agent, or Firm-Watts, l-loffmann, Fisher & l-leinke Co.

[57] ABSTRACT High lead content of uniformly dispersed; finely divided, particles is obtained in cast steel through the dissolution of lead in the steel when molten. Lead is made available for dissolution by the reducing action of steel constituents upon lead oxide (PbO) that is contained in a covering slag.

, 8 Claims, 2 Drawing Figures MOLTEN 5TEEL TAPPED FROM FURNACE INTO VESSEL D50 CONTAIN/N6 FIE/T Fuzunce we cove/2 vesset. PLACED nv arm/awe CHAMBER awe awe REDUCTION OF 0130 AND DISSOLUTION 0F LEAD $756!.

STEEL co/vrm/vwe o/ssoL 1/60 eemovso 5OL/D/F/C4T/ON WITH PEJECT/ON OF 0/5 SOLVED LEAD 45F/N8 UNIFORM DISPEES/ON PMENIEBJUW mm A 3,820,982

SHEET 1 [)F 2 MOLTEN 5TEEL TAPPED FQDM FUQNACE- /NTO l E65EL 050 CONTA/N/A/Cv FUQNACE sLAe FIE/T cove/2 VESSEL PLACED W ST/QE/NG CHAMBER ST/EElA/G EEDUCT/ON OF D50 4N0 O/SSOLUT/ON OF LEAD W STEEL.

STEEL CONTA/N/NG DISSOLt/EU LEAD QEMOVED SOLIU/F/CQT/ON W/TH PEJEcT/o/v OF D/5 SDLVED LEAD A5 F/A/E UM/FOFZM D/SPEEE/ON Fig. I

METHOD OF ADDING LEAD TO STEEL WITH LEAD OXIDE SLAG 2 RELATED APPLICATION Co-pending application of Jerry D. Thomas and Cecil B. Griffith, Ser. No. 264,012, filed concurrently herewith entitled METHOD OF PRODUCING LEADED STEEL, assigned to the assignee of this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention relates to leaded steel and processes for producing leaded steel.

2. Prior Art.

Current practices of leading steel to obtain free machining properties apparently originated in the late 1930s and early 1940s as evidenced by US. Pat. Nos. 2,182,758; 2,182,759; 2,197,259; 2,215,734 2,236,479; 2,259,342 and 3,141,767, and by United Kingdom Pat. No. 519,572. These patents basically relate to the addition of lead to different steels, certain means of making the lead addition, and the forms of the lead additive. As disclosed therein, lead is added to steel in finely divided form either in a vessel, a mold or in the pour stream as the steel is poured into a mold. A further approach, in which a stream of molten steel is fed into a bath of molten lead and allowed to over flow is disclosed in the somewhat later United Kingdom Pat. No. 894,019. Somewhat similarly, lead added to a pool of steel that fills molds in bottom pouring equipment is disclosed in US. Pat. No. 2,854,716 in an attempt to overcome objectional features and results of prior art. Notwithstanding a stated desideratum in the prior art of obtaining a highly uniform submicroscopic dispersion of a significant level of lead in steel, the fact is that leaded steels have suffered from substantial, undesirable, macroscopic, lead segregation, especially at high lead contents. This results in non-uniform distribution of the lead content in cast ingots or billets, both transversely and longitudinally, and disruption of the ingot or billet surface by large particles of lead. Such ingots require additional bottom discard practice and such steel produces inferior surface quality in machined products.

In the co-pending application of Donald F. North et al, Ser. No. 064,230, filed Aug. 17, 1970 and assigned to the assignee of the present invention, methods are disclosed and claimed for achieving a uniform submicroscopic dispersion of lead at levels up to 0.15 percent, representative of the limit of lead in steel attainable by the therein disclosed process by which lead in the form of shot or the like is added to molten steel in a vessel prior to casting. An improved method for obtaining a higher lead content with comparable uniformity and small particle size by adding lead to a molten bath in a programmed manner is disclosed in the co pending application of Jerry D. Thomas et al entitled METHOD OF PRODUCING LEADED STEEL, attorneys Docket No. 6-567, assigned to the assignee of this application. One drawback of the above improved processes is the tendency of a portion of the lead that is added to settle rather than dissolve, requiring efforts to retain such lead in the steel-containing vessel during teeming to avoid the presence of segregated lead in the cast steel.

SUMMARY OF THE INVENTION The present invention overcomes the shortcomings of the previously known processes to assure as a primary objective the production of steel in which the lead content in cast billets or ingots is essentially uniformly dispersed and finely divided and at the same time advantageously provides lead for dissolution at the surface of a molten steel bath and at a rate substantially comparable to that at which the lead is both dissolved and lost through vaporization, thus avoiding the tendency of lead introduced as shot or chunks to settle without dissolving and substantially avoiding the presence of undissolved lead at the bottom of the vessel containing the steel and reducing the risk of segregated lead appearing in the cast steel.

As in the processes disclosed in said co-pending applications, the present process comprises a combina tion of steps that make effective use of the solubility of lead in steel at temperatures above the liquidus. Upon solidification of the steel, the dissolved lead is rejected, resulting in the formation of a uniform, fine, dispersion of lead in the steel. By the improved lead addition methods of the present process there is even greater assurance that essentially the entire: lead content in the molten steel to be cast is in solution so that large particles and macrosegregation of lead in the cast ingot or billet are avoided. As a result additional bottom discard practice (elimination of lower portions of ingots that contain excess lead) is avoided, ingot loss from gross segregation and large lead particles is eliminated, and the resulting leaded steel product meets critical surface requirements.

In accordance with the present invention lead is made available for dissolution in the steel by the reducing action of steel constituents upon lead oxide PbO that is contained in a covering slag. Through stirring or agitation of molten steel in a vessel, as by induction coils, or by the turbulence of the molten steel as it flows into a vessel when the steel is tapped from a furnace, lead oxide present in or added to a. slag cover over the steel is reduced to lead at the surface of the molten steel bath by, for example, silicon in the steel. A substantial portion of the lead then dissolves into the steel.

Assuming the presence of reducing constituents in the steel, process control of the lead dissolution rate and content is achieved through the slag composition and the effective stirring of the molten steel. A production rate of lead from the oxide compatible with the dissolution rate of the lead in the steel is desired. The rate of lead production through reduction of lead oxide is a function of the lead oxide content of the slag and also depends upon the slag density; i.e., the slag must float to avoid a too rapid reduction of lead oxide. The dissolution rate of lead is primarily dependent upon the rate at which the molten steel is stirred and the extent to which lead volatiliz'ation is retarded by the slag cover, extending the time during which the dissolution reaction of lead in steel dominates the process over the lead vaporization reaction. Through proper control of the slag composition and adequate stirring, a lead production rate is achieved that minimizes or eliminates the quantity of lead that settles rather than dissolves or vaporizes. In addition the slag cover retards lead fuming.

Lead oxide is supplied as a constituent of a frit, e.g., combined with silicon dioxide along with varying amounts of other oxides. The frit alone may serve as a slag or it may be combined with a conventional furnace slag to form a composite lead oxide-containing slag, and is applied to the surface of the molten steel or is placed in a vessel prior to the introduction of the molten steel. In commercial processes a composite furnace slag and lead-oxide-containing frit is used. The lead oxide is reduced by such constituents as silicon, iron, carbon and aluminum in the molten steel to form lead and oxides of the reducing constituents. The lead in part dissolves in the steel and in part vaporizes and the oxides of the reducing constituents float into the slag. Stirring of the steel assures continued reduction and dissolution.

A principal object of this invention is to achieve a lead content in steel up to 0.26 percent by weight that is finely divided and uniformly dispersed, with a reduction in or substantial avoidance of undissolved lead in the steel and steel-containing vessel to which the lead is added.

Further objects and advantages of the invention will become apparent from the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram illustrating process steps of the present invention; and

FIG. 2 is a graph showing lead content in a steel melt as a function of time when lead is provided in the manner contemplated herein.

DETAILED DESCRIPTION In a preferred mode and exemplary process for practicing the present invention, molten steel from a furnace, such as a BOF, electric arc furnace or the like, is tapped into a vessel, such as a ladle, at as high a temperature as mill practice permits. A protective cover layer of furnace slag covers the steel in the vessel, which is then placed in suitable stirring apparatus such as the induction stirrer of a degasser. Stirring is begun and a lead oxide (PbO) containing slag or so-called frit" such as lead bisilicate (65 percent PbO, 35 percent SiO is added to the slag cover, as by depositing it onto the surface in bags. One or more additions may be made.

Certain constituents of the steel, for example dissolved silicon and aluminum, or in their absence carbon, manganese and iron, act as reducing agents to reduce the lead oxide to lead and form oxides of the reducing agents, which then float into and comprise a part of the slag. Lead so produced then dissolves in the molten steel to a limited extent may tend to settle rather than dissolved, and in part vaporizes from the slag. Thus, the rate of reduction of lead oxide, dissolution of lead in the steel settling of lead without dissolving, and vaporization of lead from the melt and the slag are interrelated or compete; the interrelationship determines the lead content in the steel, the amount of lead oxide that must be added, and the excess of undissolved lead that may exist in the vessel; and control of the process can be used to affect the interrelationship to minimize undissolved lead and maximize dissolved lead.

With a short period of time after the addition of the lead oxide, for example, to minutes, the leaded steel is teemed from the vessel to molds or to a tundish for continuous casting. Leaded steel is removed from the vessel in a manner to avoid the removal of any undissolved lead in the event some may have settled.

Lead recovery has been found to vary depending upon dissolution conditions, especially stirring, and also is sensitive to the amount of furnace slag carryover. Recovery of 40 to 52 percent of the available lead from the lead oxide added is readily obtainable as are, apparently, even higher percentages.

In a variation of the above process, lead oxidecontaining slag can be initially provided in a vessel, such as a ladle, into which steel is tapped from a furnace. The inflowing stream of steel causes turbulence within the vessel sufficient to eliminate the need for subsequent stirring and the reduction of lead oxide and dissolution of lead proceed as the steel is added to the vessel.

The amount of lead oxide in the frit and slag, the temperature of the steel, the stirring or turbulence of the molten steel during reduction and dissolution, and the time for reduction and dissolution all affect the resulting leaded steel product. Each aspect of the process is considered in more detail below.

Slag Composition and Amount The slag composition is selected to retain the lead oxide in the slag and support it on the surface of a molten steel bath by virtue of the lower density of the slag composition, and to inhibit lead fuming from the slag and bath and thereby reduce lead losses. In practice, control of the slag composition and thickness is used to control lead content in the steel, and an optimized lead oxide slag composition will produce higher lead recoveries than will other slag compositions.

In the preferred process, lead oxide (PbO) is provided as a frit, i.e., chemically combined with silicon dioxide (di) This frit can be used alone as a slag, but in a commerical process will typically be combined with furnace slag. Some examples of suitable slag compositions are listed in Table IV in connection with laboratory heats described in more detail subsequently.

To establish control over the reduction rate of the lead oxide through content and density of the slag, the invention contemplates a slag composition in which the percentage of lead oxide is adequate to react at a reasonable rate but not so high as to promote excessive vaporization of lead oxide from the slag or to increase the slag density to a point where floatation is lost. To assure this, a PbO-SiO frit is comprised of 20 to percent by weight PbO, and preferably 50-65 percent by weight PbO. Consistent therewith, the slag composition as a whole shall comprise 5 to 85 percent by weight PbO and preferably from 10 to 41 percent by weight PbO. In some instances the entire slag can be comprised of the lead oxide frit.

The amount of slag at a given lead oxide content must provide a covering layer over the molten steel of substantial thickness to prevent fuming, typically a 2 to 3 inch layer up to as much as a 12 inch layer for a to 250 ton heat. The slag must also provide a total lead quantity after the lead oxide is reduced to result in the dissolution of an amount that will equal the target quantity desired in the steel. The total slag amount and the amount of lead oxide will therefore vary with the size of the bath and the efficiency of the entire process, both in the reduction of lead oxide and in the dissolution of lead in the steel; i.e., the lead recovery rate. Determination of this rate is best achieved by taking samples of trial heats and analyzing for lead content. Examples in which this approach has been followed are set forth subsequently and can serve as an initial guide in selecting a slag composition. Time of Slag Addition, Rate of Lead Dissolution, and Stirring Lead oxide-containing frit is added to furnace slag already present on the molten steel bath is a vessel as soon as possible after the steel is tapped from the furnace to utilize the high temperature and to complete the process before the temperature drops too low. Where there is no furnace slag present, as in laboratory production, the frit can be added directly to the steel or a composite frit and conventional slag mixture can be applied. Stirring either precedes the addition or im mediately follows. In the process variation referred to above, the frit is added to a vessel prior to the introduction of steel.

the molten steel. Dissolved constituents such as silicon in the steel react with the lead oxide to produce lead and silicon dioxide and oxides of other reducing agents. The reduction rate is primarily a function of the concentration lead oxide and the reducing agents, but is also affected to some extent by the stirring rate. Lead released by the reduction reaction dissolves in the molten steel and the oxides of the reducing agents flow into the slag. If the reducing rate is too rapid as compared with the dissolution rate, settling of lead occurs. The dissolution rate is largely a factor of the rate of stirring, i.e., mechanical mixing (including mixing by such means as induction stirring, bubbling of gas, and the like) of the steel and lead, which should be vigorous, especially for higher solubility levels, such as 0.15 percent lead by weight and above. When the steel bath is stirred inductively, 6 to 10 minutes are required to dissolve0.25 percent lead by weight with vigorous stirring in a small induction furnace. Somewhat longer times will be required where larger volumes and less vigorous stirring occurs as in a plant heat stirred in a degasser. Stirring must be maintained for as long as and preferably longer than the lead oxide is being reduced. In processes ranging from small scale melts to commercial plants melts, continuous stirring after the lead oxidecontaining frit or slag is added is contemplated for a minimum of five minutes and 10 to minutes is typical. Usually no more than 30 minutes is useful. A constant, vigorous or relatively intense stirring rate is de sired, for example, of the intensity obtainable in a small induction furnace or a degasser.

The dissolution rate is also affected by the presence of the slag cover, which reduces lead losses through vaporization and thereby permits the solution reaction to continue for a greater length of time by inhibiting the dissipation of the high lead partial vapor pressure that builds up between the melt and the slag cover.

In some instances more than one addition of lead oxide-containing frit may be added to the surface of the bath, with mining after each addition.

Lead content as a function of time after the lead oxide of the frit or slag is applied to the molten steel is shown in the graph of FIG. 2 of the drawings and is discussed in more detail subsequently in connection with specific examples.

Temperature of the Steel i To assure adequate dissolution in the steel of lead released by the reduction of lead oxide during the time of reaction and dissolution, the temperature of the steel melt must be from a practical standpoint above the liquidus temperature, (which may be, e.g., 2,775 Fahrenheit and which varies with the steel composition) by at least 10 Fahrenheit at the time the lead oxide is reduced and the lead dissolves. For optimum results the temperature of the steel will be as high as mill practice will permit at the time the lead oxide is reduced, e.g., 2,900 to 3,000 Fahrenheit where the lead oxide-containing frit is applied to steel in a vessel and as high as about 3,050 degrees Fahrenheit where the steel is tapped from the furnace into a vessel already containing the lead oxide slag. Typically the slag is in contact with the molten steel for 5 to 30 minutes before the steel is cast, during which time the temperature of the steel must remain above liquidus.

Leaded Steel Products The present process is contemplated for use with a composition of steel to which lead! can be added and is especially useful in producing free: machining steels. In a preferred process, the steel can be produced in billet form by continuous casting. Alternatively, the process is also applicable to the casting of ingots or the like.

The product produced is a steel alloy having enhanced mechinability over a conventional steel without lead, but which will not have drawbacks, i.e., defects, as in conventionally leaded steel, which defects include surface and subsurface streaks of lead and blobs of lead. The product is characterized by an absence of macrosegration of lead. Reduction of lead oxide in a lead oxide-containing slag and subsequent dissolution in steel of the lead produced is utilized to produce a product having a lead content up to 0.26 percent by weight in which the predominant lead particle size will be no greater than 10 microns and the maximum lead particle size will be no greater than 30 microns. In addition, the distribution of lead throughout the product is extremely uniform, generally varying no more than 0.01 to 0.03 percent lead by weight. While nonuniformity beyond this range has been experienced, it has been attributable to the presence of undissolved lead resulting from inadequate stirring, spill-over during pouring, contamination, etc.; i.e., a failure to observe process requirements.

Analyses of laboratory heats of AISI IOL26 steel, described in more detail below, before and after the addition of lead oxide-containing slag, show a decrease in the silicon content of the steel, as shown by the following table:

TABLE I ANALYSES OF LABORATORY HEATS BEFORE AND AFTER THE ADDITION OF THE SLAG 7 TABLE I Continued ANALYSES OF LABORATORY HEATS BEFORE AND AFTER THE ADDITION OF THE SLAG Note: Carbon analyses are semi-quantitative with i 0.02 carbon accuracy. Due to analytical technique and do not necessarily reflect actual changes in carbon content.

The change in silicon content has no adverse effect on the steel product. Where the amount of certain materials that will reduce lead oxide is critical in the final 2O composition, such materials should be added after the completion of the reduction reaction. Results in Practice Examples Laboratory heats were prepared and lead additions made, which demonstrate experimentally that the present process produces high quality leaded steel, of essentially uniform lead content throughout, with a fine and uniform lead particle distribution. Observations confirm that little if any settling of lead occurs in the melt and that lead losses are predominantly through volatilization.

Five 250-pound heats were made in an induction furnace, under an atmosphere of air. Base compositions of A151 1026 and 41 18 steel were used, as follows, in percent by weight (all proportions herein being expressed in percent by weight of the steel melt unless otherwise noted):

TABLE ll Heats Nos. 1 to 4 used M81 1026 steel and heat No. 5 used A151 41 18 steel. As indicated, the melt temperature for heats 1-4 was 2,900 Fahrenheit'and slag was added to the surface of the steel in an induction furnace, which vigorously stirred the melt. The melt temperature for heat No. 5 was 3,000 Fahrenheit and the molten steel was added to a ladle during a furnace tap, the ladle already containing a lead oxide-containing slag. The compositions of the slag are shown in the following Table IV:

STEEL COMPOSITIONS C Mn Si P S Cr Mo AlSl 1026 AlSl41l1l TABLE Ill 0.035 MAX. 0.045 MAX. 0.039 0.025

THE 250-POUND LABORATORY HEATS MADE USING LEAD OXIDE-CONTAINING SLAGS Total Total Wci ht Percent Percent Temperature Weight Weight Lead in Horizontal lngot Lead Heat of Melt Addition Percent Percent PbO lngot Slice Size in Recovery No. Before Teeming Method Lead Added in Slag Edge Middle Center Pounds in lngots 1 2900F To Melt 0.30% 22.2% 0.12 0.13 0.15 72 44% in Furnace 2 2900F To Melt 0.30% 28.0% 0.15 0.15 0.17 72 52% m Furnace 3 2900F To Melt 0.30% 54.4% 0.13 0.13 0.14 72 44% in Furnace 4 2900F To Melt 0.60% 22.2% 0.23 0.24 0.25 72 40% in Furnace 5 3000F To Ladle 0.60% 75% 0.19 0.19 0.18 250 31% During Fu rnuce Pap TABLE IV COMPOSITIONS OF LEAD OXIDE SLAGS Oxide Slag Heat No. PbO SiO A1 0, CaO K20 Na,O MgO BaO ZnO Density gms/cc Commercial l Frit 1 22.2% 38.8% 9.2% 8.8% 3.2% 0.7% 0.4% 6.2% 10.5% 3.42 Lab Frit 2 28.0% 34.0% 3.3% 34.0% 0.7% Commercial Frit 3 54.4% 40.5% 4.0% 1.1% 3.89 Commercial Frit 4 22.2% 38.8% 9.2% 8.8% 3.2% 0.7% 0.4% 6.2% 10.5% 3.42 Lab Frit 5 The total weight percent of lead available from the slag was 0.30 percent in heats l-3 and 0.60 percent in heats 4 and 5. The lead oxide content of the slag varied between 22 percent by weight of the total slag and 75 percent, as shown in Table ill. Ingots of the size indicated in Table III were poured after allowing 6 to 10 minutes for reduction of lead oxide and dissolution of lead in the steel, the steel of heats 1-4 being continuously stirred during the process. The cast ingots were then analyzed for lead content and distribution. The percent recovery was lowest where the mixing depended solely upon the turbulence from the pouring of the molten steel as the furnace was tapped, in heat No. 5. in the heats Nos. 1 to 4 in which the steel was stirred inductively and the slag applied to the steel in the furnace, the lead recovery ranged between 40-52 percent.

Lead content in the cast ingots was determined on a transverse slice with an emission spectrograph at three points along a radius, one at the center of the slice, one midway to the periphery and one adjacent the periphcry. The lead content in each ingot was extremely uniform, varying predominantly only 0.02 percent by weight and in one ingot 0.03 percent. The lead was of a small particle size, having been dissolved prior to solidification of the steel.

Other tests were made where the percent recovery of lead varied from 28 percent to 80 percent or more, but difficulties in the process and an absence of data on lead distribution and in some cases a lead content beyond the solubility limit, makes the data unsatisfactory as a basis for conclusions.

Analysis of heats l to 4 before and after the addition of the lead oxide-containing slag is shown in Table l above, showing as previously mentioned, that the reduction of the lead oxide was predominantly accomplished by the silicon of the steel composition.

Lead content as a function of time was determined from pin samples of the melts taken at time intervalvs and analyzed spectrographically for lead content. A graph showing the lead content at different times for heats l to 4 is shown in FIG. 2 of the drawings, which indicates the general average rate at which the lead oxide is reduced and the lead dissolved. As indicated,

the time for dissolution was short, about 3 to 7 minutes.

Refractory vessels in which leaded steel was made in accordance with the above disclosed process and examples were crushed or broken into pieces after being emptied, and were carefully examined visually for lead particles. No lead was found in cracks or crevices of the refractory material. By contrast, vessels to which lead in finely divided form, such as shot, is added directly to a steel melt as in the processes of said co-pending appli cations, contain lead in crevices at the bottom of the vessel. It is concluded that the lead losses in the present process result from fuming and there is little or no settling of undissolved lead in the vessels containing the steel. This conclusion is reinforced by visual observations made during the application of lead oxidecontaining slag to the surface of molten steel baths, where a much higher level of lead fuming was noted as compared with melts in which lead shot is thrust through a slag layer and beneath the surface of the bath. Thus, with comparable yields of dissolved lead for a given lead addition and with higher losses through volatilization, the undesirable settling of lead is necessarily reduced.

The methods described above and the parameters involved are applicable to steel making processes in which it is desired to produce a leaded steel of high quality. It will be apparent to those skilled in the art that variations can and will be made to meet various conditions and specific data has been provided herein to provide a guide for achieving variations that may be desired. it will be appreciated, then, that while preferred embodiments of the invention have been described with particularity, the intention is to cover and secure all modifications, alternatives and equivalents within the spirit and scope of the invention expressed in the appended claims.

What is claimed is:

l. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles in the steel when solidified, including the steps of floating a slag layer on molten steel, said slag layer being comprised of at least five percent by weight lead oxide, establishing relative movement between the molten steel and the slag layer at an interface therebetween to reduce lead oxide to lead, agitating the molten steel to dissolve and disperse the lead within the steel, and thereafter solidifying the steel.

2. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles in the steel when solidified, including the steps of floating on a molten steel bath a slag layer containing a frit comprised of lead oxide (PhD) and silicon dioxide (SiO such that the composition of the slag is at least five percent by weight lead oxide (PbO), establishing relative movement between the molten steel and the slag layer at an interface therebetween to reduce lead oxide to lead, agitating the steel bath to dissolve and disperse the lead within the steel, and thereafter solidifying the steel, all in the absence of adding essentially any lead to the steel from without the slag layer.

3. A process of producing leaded steel having a uniform distribution of finely dispersed leadparticles, comprising the steps of: (a) containing molten steel in a vessel; (b) covering the molten steel with a slag cover comprised of a lead oxide-containing material; (c) stirring the molten steel to circulate the steel at the interface with the slag cover, whereby lead is produced from the reduction of the lead oxide in the slag cover by constituents of the molten steel and dissolved and dispersed in the steel; and (d) solidifying the steel.

4. The process as set forth in claim 3 wherein lead oxide comprises between 20 and 85 percent of the lead oxide-containing material and between 5 and 85 percent of the slag cover.

5. The process as set forth in claim 3 wherein lead oxide comprises between 50 and 65 percent of the lead oxide-containing material and between and 41 percent of the slag cover.

6. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles comprising the steps of: (a) containing molten steel in a vessel; (b) covering the molten steel with a slag cover that includes a frit comprised of PbO and Si0 while the temperature of the steel is at least 10 Fahrenheit above the liquidus temperature of the steel, said PbO comprising to 85 percent of the frit and 5 to 85 percent of the slag cover, the densities of both the frit and the slag being less than the density of the molten steel; (c) stirring the molten steel to circulate the steel at the interface with the. slag cover, thereby reducing PbO to lead with constituents of the molten steel and dissolving the lead so produced in the molten steel up to an amount of 0.26 percent by weight of the steel; and (d) solidifying the steel.

7. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles, comprising the steps of: (a) providing molten steel having at least one constituent suitable for reducing lead oxide to lead, (b) covering the molten steel with a slag comprised of a lead oxide-containing material. (c) creating significant relative movement between the molten steel and the slag at an interface therebetween to enhance reduction of the lead oxide by the steel, (d) agitating the molten steel to dissolve and disperse in the steel the lead resulting from the reduction, and (e) solidifying the steel.

8. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles in the steel when solidified, including the steps of floating on a molten steel bath a slag layer comprised of silicon dioxide (SiO and at least 5 percent by weight lead oxide (PbO), establishing relative movement between the molten steel and the slag layer at an interface therebetween to reduce lead oxide to lead, agitating the steel bath to dissolve and disperse the lead within the steel, and thereafter solidifying the steel.

[1 UNITED STATES PATENQI OFFICE CERTIFICATE OF CORRECTION Patent No. 3820982 Dated June 28, 1974 Inventor(s) Jerry D. Thomas and Cecil B. Griffith It is certified that error appears in the above-identified patent and that said'Letters Patent are hereby corrected as shown below:

Column 4, line 35, (di) should be (Si0 Column 7, after Table I in "*Note: there should be no period and "Due" should be due Column 9, line 52, "intervalvs" should be intervals Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) USCOMM DC 6037mm a u.s. oovznumzm PRINTING orncz; 19:9 o-sssa:u 

2. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles in the steel when solidified, including the steps of floating on a molten steel bath a slag layer containing a frit comprised of lead oxide (PbO) and silicon dioxide (SiO2) such that the composition of the slag is at least five percent by weight lead oxide (PbO), establishing relative movement between the molten steel and the slag layer at an interface therebetween to reduce lead oxide to lead, agitating the steel bath to dissolve and disperse the lead within the steel, and thereafter solidifying the steel, all in the absence of adding essentially any lead to the steel from without the slag layer.
 3. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles, comprising the steps of: (a) containing molten steel in a vessel; (b) covering the molten steel with a slag cover comprised of a lead oxide-containing material; (c) stirring the molten steel to circulate the steel at the interface with the slag cover, whereby lead is produced from the reduction of the lead oxide in the slag cover by constituents of the molten steel and dissolved and dispersed in the steel; and (d) solidifying the steel.
 4. The process as set forth in claim 3 wherein lead oxide comprises between 20 and 85 percent of the lead oxide-containing material and between 5 and 85 percent of the slag cover.
 5. The process as set forth in claim 3 wherein lead oxide comprises between 50 and 65 percent of the lead oxide-containing material and between 10 and 41 percent of the slag cover.
 6. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles comprising the steps of: (a) containing molten steel in a vessel; (b) covering the molten steel with a slag cover that includes a frit comprised of PbO and SiO2 while the temperature of the steel is at least 10* Fahrenheit above the liquidus temperature of the steel, said PbO comprising 20 to 85 percent of the frit and 5 to 85 percent of the slag cover, the densities of both the frit and the slag being less than the density of the molten steel; (c) stirring the molten steel to circulate the steel at the interface with the slag cover, thereby reducing PbO to lead with constituents of the molten steel and dissolving the lead so produced in the molten steel up to an amount of 0.26 percent by weight of the steel; and (d) solidifying the steel.
 7. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles, comprising the steps of: (a) providing molten steel having at least one constituent suitable for reducing lead oxide to lead, (b) covering the molten steel with a slag comprised of a lead oxide-containing material, (c) creating significant relative movement between the molten steel and the slag at an interface therebetween to enhance reduction of the lead oxide by the steel, (d) agitating the molten steel to dissolve and disperse in the steel the lead resulting from the reduction, and (e) solidifying the steel.
 8. A process of producing leaded steel having a uniform distribution of finely dispersed lead particles in the steel when solidified, including the steps of floating on a molten steel bath a slag layer comprised of silicon dioxide (SiO2) and at least 5 percent by weight lead oxide (PbO), establishing relative movement between the molten steel and the slag layer at an interface therebetween to reduce lead oxide to lead, agitating the steel bath to dissolve and disperse the lead within the steel, and thereafter solidifying the steel. 